Purpose of archiving- ensuring a more compact arrangement of information on a disk, as well as reducing the time and, accordingly, the cost of transmitting information through communication channels in computer networks. In addition, archiving greatly simplifies the transfer of information from one computer to another, reduces the time it takes to copy it to external media, helps protect information from unauthorized access, and helps protect against computer viruses.

The main feature of archiving- this is information compression, i.e. converting it to a form that reduces redundancy in its representation and, accordingly, requires less memory for storage.

Both one and several files can be compressed, which in compressed form are placed in one so-called archive file or archive, from where they can be extracted in their original form.

Archive file (archive) is a specially organized file containing one or more files in a compressed or uncompressed form and service information about file names, date and time of their creation or modification, sizes, etc.

The process of writing files to an archive file is called archiving(archiving, packing), and extracting files from the archive - unzipping(unzipping, unpacking).

The degree of file compression during archiving depends on its format. Some formats (for example, graphic formats) rely on compression performed by programs that create files of these types, and therefore do not shrink when archived. Best of all, when archiving, text files and database files are compressed, files of executable programs and load modules are compressed less. The compression ratio is also affected by the compression method.

In addition to regular archive files, you can create continuous, multi-volume and self-extracting archives, as well as their combinations, for example: multi-volume self-extracting, multi-volume continuous, etc.

Solid archive is an archive packed in a special way, in which all compressed files are treated as one sequential data stream.

Continuous archiving greatly increases the compression ratio, especially when adding a large number small similar files. However, there are also disadvantages:

§ existing continuous archives are updated more slowly than regular archives;

§ encrypted non-stop archives cannot be modified;

§ To extract a single file from a continuous archive, it is necessary to analyze all previous archived files, so extracting individual files from the middle of a continuous archive is slower than extracting from a normal archive. However, if all or a few of the first files are extracted from a continuous archive, then in this case the decompression speed is almost the same as with ordinary archives;

§ If any file in a continuous archive is damaged, then all files following it will also fail to be extracted. Therefore, when saving a continuous archive on unreliable media, it is recommended to add recovery information.

Continuous archives are best used when:

§ the archive is rarely updated;

§ there is no need to frequently extract one or more files from the archive;

§ one is archived big file;

§ Compression ratio is more important than compression speed.

Files in continuous archives are usually sorted by extension, but the sort order can be changed.

Multi-volume archives are archives consisting of several parts (volumes). Typically, volumes are used to store a large archive on multiple floppy disks or other removable media.

The first volume in the sequence has the usual standard extension archiver program, and extensions of subsequent volumes - the first letter of the archiver extension and a serial number.

Files in existing volumes cannot be added, updated, or deleted.

Self-extracting (SFX, from English words SelF-eXtracting) archive is the archive to which the executable is attached. This module allows you to extract files by simply running the archive as regular program. Thus, no additional external programs are required to extract the contents of an SFX archive. SFX archives, like any other executable files, usually have the .EXE extension, but they can be handled just like any other archive.

SFX archives are useful in cases where you need to transfer the archive to someone, but you are not sure that the recipient has the appropriate archiver to extract files.

Multi-volume and self-extracting archives can also be continuous.

Programs that archive / unzip files are called archiving programs.

Archiving programs can be compared according to the following main parameters: interface, compression methods (determining the degree of file compression), types of archives created, speed, support for other archiver formats.

When creating an archive, the archiver program automatically assigns its own extension to the archive file, for example, zip, rar, etc.

The archiving program is managed in one of the following ways:

1. using command line;

2. using the built-in shell and dialog panels that allow you to control using menus and function keys.

3. using function key combinations in operating shells, which, as a rule, can offer a choice of several DOS archiving programs or the shell's own archiver.

4. using GUI elements.

Despite the many archiving programs, a modern user, as a rule, really works with two archive formats: ZIP and RAR.

The degree of information compression depends on several reasons:

First, the type of data being compressed is of great importance. Graphic and text files are best compressed. For them, the compression ratio can be from five to forty percent. Files of executable programs, boot modules, multimedia files are compressed worse.

Secondly, the compression method is of great importance.

Thirdly, it is also important which archiver is used. When choosing the type of archiver, they are usually guided by the following considerations: so that the compression ratio is as high as possible, and the time it takes to pack and unpack files is as short as possible.

Information compression programs

Compression occurs with the help of archiving programs. To date, the most common are four archivers - WinRar, WinAce, 7Zip and WinZip. As for the last program, it does not stand up to scrutiny.

Let's take a closer look at the archiver - WinRar This archiver can be associated with the following file types: RAR, ZIP, CAB, ARJ, LZH, ACE, 7-Zip, TAR, GZip, UUE, BZ2, JAR, ISO.

The program supports files of almost unlimited size (up to 8,589,934,591 GB). True, to work with files larger than 4 GB, you need to work in file system NTFS.

When choosing optimal settings There are a few things to keep in mind for compression:

Although WinRAR supports the ZIP format, it is recommended to choose RAR in most cases. This will provide more high level compression. You can compress files to ZIP if you are not sure that a program will be installed on the computer on which the files will be unpacked, with which you can unpack files in RAR format.

You need to decide which compression method is best to use. The higher the compression ratio, the more time it will take to archive, so here you need to consider for what purposes the data is archived. If this is long-term storage, of course, it makes sense to wait and get the archive with the maximum compression ratio, but if you just need to send a few documents by mail, the normal (Normal) compression ratio is fine for you.

If you need to achieve maximum file compression, use the Create solid archive option. However, it also has its drawbacks. Firstly, it will take more time to unpack such files than to extract from a regular archive. Imagine that you have two hundred files in your archive. If it's created in the usual way, you can easily extract one of the files. If you used solid archive, then it will matter how the file you need would be archived. If it was in the middle of the second hundred, then to unpack it, the program will need to unpack 150 files before it gets to it. Creating archives in this way can also entail great losses, because if the archive becomes corrupted, you will lose all the files that were in it. In the case of packing in the usual way, you can extract from the damaged archive, if not all, but most of the files.

If you need to create a large archive, this can take quite a long time. WinRar allows you to determine how much time it will take to complete a particular task. The Benchmark and hardware test option is intended for this. Another reason to use this option is to define possible errors, which may occur during archiving on a computer of a particular configuration due to a hardware failure.

Among other settings of WinRar "a, one can note the possibility of creating self-extracting archives with an indication of the unpacking path. Such files do not require an archiver program on the computer on which they are planned to be unzipped. Such archives are called SFX-archives. Their disadvantage compared to conventional archives files is a larger size, since they, in addition to the actual packed files, also contain the EXE executable module.

The contents of a RAR archive can be made invisible. To do this, in the program settings, in the Archiving with Password window, you need to check the box next to the Encrypt File Names line.

You can also set a password to open the archive. As a result of an error in transferring an archive over a local network or downloading it from the Internet, as well as due to a hardware failure or a virus attack, the archive may be damaged. WinRar allows you to determine the integrity of the data by testing the archive using the Test Archived Files option.

To minimize the chance of data loss, when creating WinRar archives it is recommended to use the Put Recovery Record option (this checkbox can be found on the General tab of the archive creation window).

If this has been done, then in case of damage to the archive, it can be restored.

In addition, in WinRar, you can reduce the likelihood of damage to a RAR archive by specifying the size of the information to be restored when creating it. To do this, you need to execute the Commands > Protect Archive From Damage command in the Winrar window. At the same time, the volume of the Recovery Record cannot exceed ten percent of the total size of the archive.

To repair damaged RAR archives, select the required file in the WinRar window and execute the Tools > Repair command.

WinRAR can be built into the context menu, and it supports not only the Explorer menu, but also other programs, such as the popular file manager Total Commander. This makes it possible to quickly archive files using the default settings and without opening the program window for this. By the way, the default settings can be changed, in accordance with what requirements you place on your archives. You can do this by opening the WinRar window and executing the Options > Settings command. In this window, go to the Compression tab and click the Create Default button. The settings specified in this window will be used for quick archiving. If you need to change the archiving settings, this can also be done using context menu. To do this, select the Add to Archive… command. Here you can set the format and compression ratio, specify the name of the archive, and select other archiving options.

WinRar allows you to save user-defined settings to a file with a Reg extension. Later, this file can be imported into the program to reuse the given configuration. This file stores information such as the history of archives that have been created recently, default compression settings, etc.

Another handy Winrar option is the ability to create your own bookmarks - Favorities. It is very often necessary to regularly back up the same folders on your hard drive. By bookmarking information about the location of these folders, you can quickly navigate to them in the program window and back up the necessary files and subdirectories.

General information about archiving files

• using the MS DOS command line, which forms run command, containing the name of the archiver program, the control command and its configuration keys, as well as the names of the archive and source files; such management is typical for archivers ARJ, AIN, ZIP, RAK, LHA, etc.;

• using the built-in shell and dialog panels that appear after starting the program and allow you to control using the menu and function keys, which creates a more comfortable working environment for the user. Such control has a program - RAR archiver.

• create archive files from individual or all files of the current directory and its subdirectories, loading up to 32000 files into one archive;

• add and replace files in the archive;

• extract and delete archive files;

• protect each of the files placed in the archive with a 32-bit cyclic code, test the archive, checking the safety of information in it;

• receive work assistance in 3 international languages;

• enter comments to files in the archive;

• save paths to files in the archive;

• save several generations (versions) of the same file in the archive;

• reorder the archive file by file sizes, names, extensions, date and time of modification, compression ratio, etc.;

• search for strings in archived files;

• restore files from damaged archives;

• create self-extracting archives both on one volume and on several volumes;

• view the contents of text files contained in the archive;

• ensure the protection of information in the archive and access to files placed in the archive with a password.

• the ability to work in two modes - full screen interactive interface and conventional command line interface;

• support for other types of archives; in full-screen mode, RAR provides the ability to work with archives of other types (.ZIP, .ARJ, LZH), view their contents, modify and convert them;

• using the highly efficient solid compression method to obtain a high compression ratio (10 - 50% higher than usual);

• the ability to create self-extracting and multi-volume archives;

• password protection of archives.

• password encryption;

• adding file and archive comments;

• the possibility of partial or complete recovery of damaged archives;

• protection of the archive from changes;

• the ability to add to the archive information about the creator of the archive, the time and date of the last changes made to the archive.

• in command line mode;

• in full screen mode.